> I think that if your theory is that the quality is in the sum total of all differences with other works, then it's not saying much.

I wouldn't say that quality and value are the same thing. Oftentimes works of questionable quality are incredibly valuable because they open up new domains for other artists to develop.

> On the surface, texts are unique as snow flakes, so that's not a useful perspective.

This isn't true at all. In fact, most people, even trained critics, have trouble telling writers apart, let alone texts. There are exceptions, of course -- mostly the avant-garde, because you know when you're reading Joyce or Pound -- but even then the vast majority of people can't distinguish the real thing from a parody. When I was in grad school a quiz (http://reverent.org/poetry_or_parody.html) made its way through our poetry seminar, and it was hilarious. Two of us missed only one; the rest missed at least six! I just retook it now, three years later, and missed three, so I guess I'm losing my touch.

> Some differences or features will surely play a larger role than others in determining quality.

Of course, but again, quality <> value. Also I'm not sure what you're responding to with this thought. There's nothing about 'sum totals' or anything like that in the Perkins quote, and I don't think I suggested it elsewhere.

> For the features that matter, commonalities might be more interesting than differences.

Do you have an example? The 'might' is important here: I agree that it's possible, but I can't think of an example. Most likely I would think the commonality would be some shared trope that the text then proceeds to spin off in an entirely different direction, so that the commonality is only interesting as staging for the difference. But I can be persuaded otherwise.

> I think there might not be an effective difference between a particular interest acting like a filter, and the rest of the differences identifying a work. They appear to be different because the former is explicit and particular, but in the end our taste is conceivably described as a filter.

I'm not sure if this is what you meant, but I think it's an interesting point: namely, that every difference is a difference from, so by shifting the context in which a work is understood, you've effectively changed what its commonalities with and differences from other works are. And that leads us down the oh-so-tricky rabbit hole of establishing contexts, e.g. via period (Romanticism), tradition (form, genre), and so on.

As far as taste being a filter, that just depends on the person. It's certainly possible to imagine tastes that can't be used as filters because they don't involve surface properties like genre trappings.

> You seem to suggest that shared features automatically imply genre works which are typically deemed of lower value.

I'm not suggesting either of those things. Shared features don't imply genre works (all works have shared features), and genre works aren't necessarily of lower value (they just attract certain audiences regardless of their value).

> If artistic value is said to only reside in an ineffable difference of the whole work

It's neither ineffable nor anything to do with the 'whole' work. I'm sure it seems abstract, with us talking about all of art in one go here, but once you get down to specific texts and contexts any competent critic is going to talk in excruciating detail about what specifically is valuable in a given work. At least, that's the idea -- in practice most professional critics are crap.